1. Field of the Invention
The present invention relates generally to methods and apparatus for monitoring the penetration distance of an elongate device inserted into a body lumen during a medical procedure. More particularly, the present invention relates to real time detection and position monitoring of the device as it passes by a location fixed relative to the lumen.
Catheters, esophageal probes, endoscopes, and other medical devices are frequently introduced into body lumens for a variety of purposes, including imaging and interventional therapy. For many such procedures, it is necessary to accurately monitor the position of the catheter, particularly the distal end of the catheter which is remote from the entry point. For example, it is frequently necessary to know the precise location of the distal tip of a device in order to perform a subsequent interventional procedure, to facilitate interchange of devices, and to track the precise location of a device during the course of a single procedure.
The most common positional monitoring techniques rely on fluoroscopic imaging of radiopaque markers on the device. While such fluoroscopic techniques are well suited for observing the progress of a device as it is being inserted, particularly for monitoring the manipulation of intravascular catheters through various branches of the vascular system, such techniques are limited in several respects. In many situations, fluoroscopic imaging equipment is not available and it would be desirable to have other means for providing accurate, real time monitoring of device penetration. Moreover, a visual fluoroscopic image is difficult to record to provide a permanent record of device position. Such visual positional information is also inaccurate since the apparent location of the distal end of a device may change depending on the patient's position relative to the imaging equipment. Additionally, fluoroscopic images can be difficult to coordinate with images produced by other procedures, particularly ultrasonic imaging procedures which employ a separate CRT screen presenting a quite different view of the imaged area.
Heretofore, the penetration depth of elongate medical devices, such as catheters and probes, has usually been monitored visually by the physician observing scale markings which have been placed on the side of the device. That is, the physician will simply look at the device at the point of entry and read the approximate penetration depth from the scale. While this approach has the advantage of simplicity, it does suffer from numerous limitations which restrict its effectiveness in modern medical procedures.
First, the accuracy of penetration which can be determined is limited by the lack of a fixed location against which to read the scale. The accuracy is further limited by the relatively broad spacing between scale markings which are required to permit visual reading. The visual reading of the scale further requires that the physician turn away from other areas where attention should be directed and attempt to read the markings, often in diminished light as required by many procedures. Each reading which is obtained requires additional time to be recorded and becomes obsolete as soon as the device is moved in any fashion. As a result, coordination between the penetration depth at any given time and other images can be problematic. Finally, the visual reading of a penetration depth does not lend itself to permanent recording, particularly in combination with other imaging techniques, such as ultrasonic images which are frequently recorded on video tape.
For these reasons, it would be desirable to provide improved methods and systems for monitoring intraluminal penetration depth of medical devices used during various medical procedures. Such monitoring should provide very accurate determination of depth, preferably on a real time basis. The system should be highly repeatable so that the devices can be withdrawn, interchanged, and reintroduced with assurance that the distal end of the device will be returned precisely to a desired location. The penetration depth information should be provided in a form which is amenable to digital display, recording, and preferably to recording in combination with other imaging procedures, such as ultrasonic imaging procedures. Additionally, the depth monitoring should not require effort of the physician beyond reading a convenient display of penetration depth, optionally in combination with other imaging information.
2. Description of the Background Art
U.S. Pat. No. 5,004,456, describes an anesthetic administration catheter having spaced-apart markings along its length to provide a visual indication of penetration depth. U.S. Pat. No. 3,399,668, describes a cholangiography catheter having equally spaced-apart indicia to permit the physician to determine the extent of insertion. U.S. Pat. Nos. 4,838,879, and 4,279,252, describe catheters having spaced-apart opaque rings along their lengths to permit calculation of image magnification. U.S. Pat. No. 3,605,750, describes an endotracheal tube having three designations along its length corresponding to three particular penetration depths. U.S. Pat. Nos. 4,431,005; 4,416,289; 4,096,862; and 3,847,157, describe catheters having magnetic and radioactive markers which can be located using external monitoring equipment.